The present invention relates to extruders, and specifically the present invention relates to an extruder with an extruder barrel surrounded by a jacket with multiple zones each of which may be either heated or cooled.
In extruding rubber or plastic materials it is common to provide an extruder barrel with a jacket through which a heat transfer medium, usually water, is pumped. The jackets are divided into a number of different zones each covering a successive axial span along the length of the extruder barrel. Fluid, either hot or cold, is circulated through each zone to heat or cool the extrudate in the particular zone as required. Temperature responsive controls are provided to regulate the flow of fluid through the various jacket zones.
In these prior art extruders, each zone may have its own heating means and cooling means. Typically, a temperature control unit has a pump and two heat exchangers for each zone, one heat exchanger for heating and one for cooling. Valves direct the pumped liquid from one of the zones through one of the heat exchangers and back to the zone. Which heat exchanger is used depends on whether the zone requires heating or cooling. The two heat exchangers associated with each zone are not normally used simultaneously.
In addition to the inefficiency of using only one half of the heat exchangers at a time, excess capacity to heat or cool one or more zones is expensive to achieve. Typically, during extrusion of rubber or plastic some zones, say two out of five, may need cooling while the remaining zones may need heating. Which zones need which and how much may vary during an operational run of the extruder and between runs extruding different materials. In order to provide flexibility and some reserve capacity the heat exchangers and pump associated with one or two of the different zones of prior art temperature control units have been oversized. These would then be connected with any jacket zone that required extra heat or cooling. Such systems then required connecting and reconnecting of the temperature control unit with the extruder barrel whenever the jacket zones required extra heating or cooling capacity.